Polarizing plate and liquid crystal display device using the same

ABSTRACT

A polarizing plate including a polarizing layer having a thickness of about 20 nm to about 1500 nm formed by rubbing at least one surface of a substrate, coating the rubbed surface of the substrate with an aqueous solution containing a dye having a tabular molecular shape, and drying the solution. This polarizing plate is a thinner polarizing plate with a high degree of polarization and suitably applicable to portable electronic equipment such as cellular phones, portable information terminals, smart cards and IC cards.

This is a continuation of application Ser. No. 10/062,437 filed Feb. 5,2002; now U.S. Pat. No. 6,965,473 the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polarizing plate, a polarizing platehaving a reflecting layer and a polarizing layer, and a liquid crystaldisplay device using such a polarizing plate.

2. Description of the Related Art

Liquid crystal display devices have found applications in various fieldsincluding not only notebook type personal computers, word processors andmonitors of desktop type personal computers, calculator, watch, but alsoliquid crystal projectors, liquid crystal TV sets, digital cameras,electronic notebooks, personal digital assistances, amusement equipment,stationery equipment, cellular phones, car navigation systems, andhousehold electrical appliances such as rice cookers, air conditionersand microwave ovens.

With this widespread use of liquid crystal display devices, a variety ofrequirements have been made for polarizing plates as a requisitecomponent for the liquid crystal display devices.

As a polarizing plate, generally known is one constructed of aniodine-based polarizing film or a dye-based polarizing film made byadsorbing iodine or a dichroic direct dye to a polyvinyl alcohol resinfilm in an oriented manner, with transparent protection films such astriacetyl cellulose films laminated to both sides of the polarizingfilm. The thickness is about 6 μm to about 30 μm for the polarizing filmmade of a polyvinyl alcohol resin, and is totally about 100 μm to about190 μm including the transparent protection films. This polarizing filmis produced by uniaxially stretching a polyvinyl alcohol resin film,adsorbing iodine or a dichromatic direct dye having an azo group to thefilm in an oriented manner, and soaking the resultant film in an aqueoussolution containing boric acid.

Demand for lighter and thinner devices has been made for portable liquidcrystal display devices such as cellular phones, electronic dictionaryand personal digital assistances. With this demand, thinner polarizingplates have been required.

Reflective polarizing plates and semi-transmission reflective polarizingplates are often used for portable liquid crystal display devices. Asreflecting plates or semi-transmission reflecting plates used forreflective polarizing plates and semi-transmission reflective polarizingplates, often used are scattering-type reflecting plates orsemi-transmission reflecting plates constructed of a matted film havinga thickness of about 50 μm with aluminum or silver deposited to one sideof the film, and mirror-reflection reflecting plates orsemi-transmission reflecting plates combined with a light diffusionlayer. However, reflective polarizing plates including such reflectingplates are thick and for this reason easy to cause parallax. Thinnerreflective polarizing plates are therefore requested.

As a thin polarizing plate, a polarizing plate having a polarizing layerformed by coating a solution containing a dye to a substrate has beenknown. For example, Japanese Laid-Open Patent Publication No. 3-54506(JP 3-54506 A) discloses a polarizing plate having a polarizing layerformed by rubbing and then corona-treating a substrate and coating thetreated surface of the substrate with a dichromatic dye having a rodmolecular shape to arrange the dye molecules on the substrate in thecoating direction. This polarizing plate, however, failed to becommercialized because the polarizing performance was insufficient. U.S.Pat. No. 6,049,428 discloses a polarizing plate improved in polarizingperformance from the conventional coating-type polarizing plate. Thispolarizing plate is formed by coating a solution containing a dye to asubstrate, which solution is prepared by introducing at least onehydrophilic groups to the dye having a tabular molecular shape andsolving the resultant dye to water. However, the polarizing performanceof this polarizing plate is still insufficient. Further improvement intransmittance and contrast is therefore requested.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a polarizing plateexcellent in contrast, thinned and improved in degree of polarization byusing a polarizing layer obtained as a coating of an aqueous solutioncontaining a dye having a tabular molecular shape. Another object of thepresent invention is to provide a reflective polarizing plate or asemi-transmission reflective polarizing plate having an above mentionedreflection layer and a polarizing layer, which can be thinner than theconventional devices.

To attain the above objects, the inventors of the present invention haveearnestly examined and found that a thin polarizing plate havingsatisfactory polarizing performance can be obtained by coating a rubbedsurface of a substrate with an aqueous solution containing a dye havinga tabular molecular shape. The present invention has been realized basedon the above findings.

That is, the present invention is to provide a polarizing platecomprising a polarizing layer having a thickness of 20 nm to 1500 nmformed by rubbing at least one surface of a substrate, coating therubbed surface of the substrate with an aqueous solution containing adye having a tabular molecular shape, and drying the solution.

In another aspect, a reflective polarizing plate is provided, in which areflection layer is formed on one surface of a substrate and an abovementioned polarizing layer having a thickness of about 20 nm to about1500 nm is formed on at least one surface of the substrate. Thereflective polarizing plate may also include a light diffusion layer onthe polarizing layer. The reflective polarizing plate can be placed on aliquid crystal cell with the polarizing layer being positioned closer tothe liquid crystal cell, to attain a reflective or semi-transmissionreflective liquid crystal display device.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given herein below and accompanying drawings whichare given by way of illustration only, and thus are not limitative ofthe present invention and wherein:

FIG. 1 is a schematic cross-sectional view of an example of layerconfiguration of a polarizing plate having a reflecting layer of thepresent invention;

FIG. 2 is a schematic cross-sectional view of an example of layerconfiguration of the polarizing plate having a reflecting layer and adiffusing layer of the present invention;

FIG. 3 is a schematic cross-sectional view of another example of layerconfiguration of the polarizing plate having a reflecting layer of thepresent invention;

FIG. 4 is a schematic cross-sectional view of another example of layerconfiguration of the polarizing plate having a reflecting layer and adiffusing layer of the present invention;

FIG. 5 is a schematic cross-sectional view of an example of laminationof the polarizing plate of FIG. 1 to a liquid crystal cell;

FIG. 6 is a schematic cross-sectional view of an example of laminationof the polarizing plate of FIG. 2 to a liquid crystal cell;

FIG. 7 is a schematic cross-sectional view of an example of laminationof the polarizing plate of FIG. 3 to a liquid crystal cell;

FIG. 8 is a schematic cross-sectional view of an example of laminationof the polarizing plate of FIG. 4 to a liquid crystal cell.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described in detail.

According to the present invention, a transparent resin film isgenerally used as a substrate for forming a polarizing layer. Examplesof such a transparent resin film include cellulose films, polyesterfilms, polyolefin films, acrylic films, polycarbonate films, polyarylatefilm and polyether sulfone films. To be more specific, as cellulosefilms, cellulose acetate films are preferred, including a cellulosetriacetate film and a cellulose diacetate film, for example. Polyesterfilms include a polyethylene terephthalate film, a polyethylenenaphthalate film and a polybutylene terephthalate film, for example. Aspolyolefin films, amorphous ones are preferred. In particular, preferredare those having cyclic olefin polymerization units such as norborneneand polycyclic norbornene monomers. Copolymers of cyclic olefin andchain olefin may be used. Among others, films made of norbornene resinscan be used advantageously. Ones having a polar group are alsoeffective. A glass plate or a metal plate may also be used in place ofthe resin film.

The substrate is preferably as thin as possible, but, if it isexcessively thin, the workability degrades. Therefore, the thickness ofthe substrate may be about 10 μm to about 150 μm, preferably about 20 μmto about 100 μm, more preferably about 30 μm to about 90 μm. Thesubstrate may contain a UV absorber and the like. As such a substrate, acommercially available product may be used. Examples of commerciallyavailable triacetyl cellulose films include “KONICA® UV80SF” from KonicaCorp. and “FUJITAC®” from Fiji Photo Film Co., Ltd. Examples ofcommercially available amorphous polyolefin rein films include “S-SINA®”and “SCA40” from Sekisui Chemical Co., Ltd., “ARTON®” from JSR Corp.,“ZEONEX®” and “ZEONOR®” from Nippon Zeon Co., Ltd., and “APO®” and“APEL®” from Mitsui Chemicals, Inc. The substrate is preferablynon-oriented and has an inplain retardation value of about 100 nm orless, more preferably about 50 nm or less. Note that this value is notapplied when a resin film having a phase retardation property is used asthe substrate. Viewing angle enlarged films, such as “FUJI WVA FILM”from Fuji Photo Film Co., Ltd. and “LC FILM” and “NH FILM” from Nipponpetrochemicals Co., Ltd., can also be used as the substrate althoughthey have a birefringence property. “DBEF”, “TDF” and “DRF” from 3M, canalso be used as the substrate.

According to the present invention, at least one surface of thesubstrate described above is coated with an aqueous solution containinga dye having a tabular molecular shape to form a polarizing layer. Priorto this coating, the surface of the transparent substrate to be coatedis subjected to rubbing. It is presumed that some orientation isprovided on the surface of the substrate by this rubbing and this causesthe dye having a tabular molecular shape in an aqueous solution appliedto the surface to be oriented roughly in one direction. In thepolarizing plate of the present invention, the dye having a tabularmolecular shape is oriented roughly perpendicular to the rubbingdirection. The direction of orientation of the dye molecules in thepresent polarizing layer unexpectedly differs from that in the knownpolarizing layer as disclosed in JP 3-54506 A, in which the direction oforientation of the dye molecules corresponds to rubbing direction.

The surface of the substrate can be rubbed with a velvet cloth or thelike, for example. The cloth used for the rubbing may be made of rayon,cupra, nylon, cotton, or felt, for example. The cloth may be woundaround a roll and rotated for rubbing, or the cloth may be fixed whilethe substrate is moved for rubbing. The rubbing is performed in aconstant direction on the surface of the substrate, and must beperformed at least once. The surface may be rubbed several times, andeven be rubbed in a reciprocating manner in constant directions. When along size substrate is rubbed, it is preferable that rubbing isconducted by pressing the cloth to the substrate. Though the travelingdirections of the roll and the substrate may be same or reverse each toother in the case of using the cloth wound around a roll, the samedirection is preferable because uniform rubbing can be easily carried.

The thus-rubbed surface of the substrate is coated with an aqueoussolution containing a dye having a tabular molecular shape to form apolarizing layer. Examples of such dyes include an anthraquinone typedye, a phthalocyanine type dye, a porphyrin type dye, a naphthalocyaninetype dye, a quinacridone type dye, a dioxadin type dye, an indanthrenetype dye, an acridine type dye, a perylene type dye, a pyrazolone typedye, an acridone type dye, a pyranthrone type dye and an isoviolanthronetype dye.

They are dyes having a tabular molecule shape like a disk, representedby the following structural formula, for example.

wherein R, R′ and Y represent substituents.

The dyes having a tabular molecular shape suitably usable for thepresent invention are disclosed in U.S. Pat. No. 5,739,296.

In the present invention, an aqueous solution containing a dye isprepared by introducing one or a plurality of hydrophilic groups such assulfonic acid groups into the above dyes having a tabular molecularshape and dissolving the resultant dye to water. The dye introducedhydrophilic groups is amphipathic material exhibiting a lyotropic liquidcrystal phase.

As an aqueous solution containing such a dye, one prepared by Optiva,Inc. in US may be used.

The aqueous solution containing a dye for coating preferably contains asurfactant in addition to the dye. Examples of the surfactant includepolyethylene glycol and “TRITON® X-100” (a nonionic surfactant availablefrom Rohm and Haas Co.).

Coating with the aqueous solution containing the dye can be performed bya normal method. For example, Meyer bar coating, gravure coating, dyecoating, dip coating, screen-printing and printing techniques such asink-jet printing may be used. Among them, a method providing shearstress to the aqueous solution is preferably used. After the coating,water as the solvent is evaporated to form the polarizing layer. Watercan be evaporated by a normal drying method including heat drying, roomtemperature drying, freeze-drying and far-infrared drying. The thicknessof the resultant polarizing layer is as thin as about 20 nm to about1500 nm, preferably about 50 nm to about 1000 nm, which is properlyselected depending on the type of the dye having a tabular molecularshape and the transmittance of the resultant polarizing plate.

The thus-obtained polarizing plate can be placed on one or both of thesurfaces of a liquid crystal cell, as is the case in the conventionalpolarizing plate, to obtain a liquid crystal display device. Thepolarizing plate can be used as a front polarizing plate or a backpolarizing plate for a liquid crystal cell. When the polarizing plateobtained according to the present invention is placed on a so-calledplastic liquid crystal cell or film liquid crystal cell having twopolymer films attached to each other to obtain a liquid crystal displaydevice, the polarizing plate of the present invention may be bonded tothe liquid crystal cell, or the polymer films constituting the liquidcrystal cell themselves may be made of a member including a thinpolarizing layer formed on a surface of a substrate according to thepresent invention.

As shown in FIG. 1, the polarizing plate of the present invention mayinclude a reflecting layer 3 on one surface of a substrate 1 and apolarizing layer 5 on the other surface of the substrate 1. A lightdiffusion layer 7 may also be provided on the surface of the polarizinglayer 5 opposite to the substrate 1 as shown in FIG. 2. The substrate 1may be a translucent or milky resin film. As another configuration ofthe polarizing plate of the present invention, the polarizing layer 5may be directly formed on the reflecting layer 3 as shown in FIG. 3. Thereflecting layer 3 is normally formed on a surface of the substrate 1.In this case, the reflecting layer is formed on a surface of thesubstrate, next, a surface of the resultant reflecting layer is rubbedand a polarizing layer is formed on the rubbed surface of the reflectinglayer. A light diffusion layer 7 may also be provided on the surface ofthe polarizing layer 5 opposite to the surface thereof in contact withthe reflection layer 3 as shown in FIG. 4.

The reflecting layer 3 is preferably constructed of a metal layer forgood reflection of light. Such a metal layer can be provided withforming a layer made of a metal having high reflectivity, such asaluminum and silver. The metal layer may be formed by a normal methodused for forming a metal thin film, including vacuum evaporation,sputtering and ion plating, for example. In general, the reflectinglayer 3 having a thickness of about 10 nm to about 100 nm exhibitspractically sufficient reflectivity. The reflecting layer 3 may be asemi-transmission reflecting layer provided with some degree oftransmission. The thickness of the metal layer provided withtransmission is normally about 10 nm to about 30 nm.

When a layer made of silver is formed as the metal layer by evaporationor the like, a protection layer is preferably formed on the top and/orbottom of the metal layer to prevent degradation of the metal layer. Asthe protection layer, there is no specific limitation, but coat filmsmade of acrylic resins, epoxy resins, polyester resins, urethane reins,alkyd resins and the like may be preferably used, for example. Suchprotection coat films can be formed by a normal method including rollcoating, gravure coating and spraying. A thin film made of an inorganicmatter such as aluminum oxide and silicon oxide may also be used as theprotection layer. The protection layer normally has a thickness of about5 μm to about 20 μm, if provided.

The reflection surface of the reflecting layer 3, that is, the interfacewith the substrate 1 may be roughened. For example, the surface can beroughened by a method of sandblasting the surface of the substrate 1before formation of the reflecting layer 3 or a method of coating thesurface of the substrate 1 with a coat solution containing inorganicparticulates or organic particulates. Alternatively, a resin film madeby flattening a resin with inorganic fillers mixed therein by extrusionor the like may be used as the substrate because the surface of theresin film is rough.

When the reflection surface of the reflecting layer 3 is a flat mirrorsurface, the light diffusion layer 7, made of a resin with inorganicparticulates and/or organic particulates mixed therein, may be providedon the polarizing layer 5 as shown in FIG. 2. Examples of the inorganicparticulates used in this case include not only particulates of silica,calcium carbide and the like, but also iridescent particulates of pearlpigments such as synthetic or natural mica coated with titanium dioxide,tabular fish scale foils, and hexagonal plate basic lead carbonate andthe like. Examples of the organic particulates include acrylic beadssuch as polymethyl methacrylate beads, polystylene beads such ascross-linked polystylene beads, polycarbonate beads,melamine-formaldehyde resin beads, benzoguanamine-formaldehyde resinbeads and organic silica beads. The particle size of the particulates isnot specifically limited, but may be about 0.1 μm to about 50 μm,preferably about 1 μm to about 20 μm, more preferably about 1 μm toabout 10 μm. The above particulates may be used alone or in combinationof two or more types. The resin for the light diffusion layer 7 is notspecifically limited, but may be any of acrylic resins, urethane resins,epoxy resins, polyester resins, alkyd resins and the like. These resinsmay have a viscosity property. The combination of the particulates andthe resin binder may be appropriately selected. Preferably, thecombination is selected so that the difference in refractive indextherebetween is about 0.01 to about 0.5. The mixture ratio of theparticulates to the resin binder is not specifically limited, either,but in general, about 0.01 to about 70 parts by weight of theparticulates are mixed in 100 parts by weight of the resin binder. Whenthe light diffusion layer 7 is provided, the thickness of this layer isnormally about 1 μm to about 100 μm, preferably about 5 μm to about 30μm.

The light diffusion layer 7 can be formed by mixing the particulates inthe resin and then applying the mixture by a normal method such as rollcoating, gravure coating and straying, for example. Alternatively, thelight diffusion layer 7 may be formed with laminating a film having alight diffusion property. Such a film having a light diffusion propertycan be obtained using the inorganic particulates and/or organicparticulates and the resin described above. For example, it may be afilm obtained by casting the resin with the particulates mixed therein,a film obtained by first coating a surface of a substrate film with theresin with the particulates mixed therein and then peeling off the resinfrom the substrate film, a film obtained by embossing the surface of anyof the above films, or a film obtained by subjecting a mixture of resinsdifferent in refractive index to thermosetting or photo-curing. Theresultant light diffusion film may have a haze value of about 5% toabout 99%, for example. The way of laminating the film is notspecifically limited. For example, the film may be laminated in a normalway using an acrylic adhesive or the like.

The thus-obtained reflective polarizing plate can be laminated on theback surface of a liquid crystal cell (surface opposite to that on theviewer's side) to obtain a liquid crystal display device. In thisplacement, the reflective polarizing plate is positioned so that thepolarizing layer is closer to the liquid crystal cell as shown in FIG. 5to FIG. 8. A phase retardation plate may be interposed between thepolarizing layer 5 or the light diffusion layer 7 and the liquid crystalcell 9 as required. Another polarizing plate (not shown) may be placedon the front surface of the liquid crystal cell 9 (surface opposite tothat on which the reflective polarizing plate is placed). The frontpolarizing plate may be one including a normal polyvinyl alcoholpolarizing plate, but may be a polarizing plate according to the presentinvention including a polarizing layer comprising the dye and having athickness of 20 to 1500 nm formed on a substrate by coating, to attainfurther thinning of the polarizing plate. In the latter case, thepolarizing layer is normally positioned as the outermost layer. A phaseretardation plate may also be placed on the front side of the liquidcrystal cell.

EXAMPLES

Hereinafter, the present invention will be described in more detail byway of examples. It should be noted that the present invention is notrestricted by these examples.

Single transmittance Ts(λ), parallel transmittance Tp(λ) and crossedtransmittance Tc(λ) for an arbitrary wavelength were calculated usingexpressions (1), (2) and (3) below.Ts(λ)={K(λ)+L(λ)}/2  (1)Tp(λ)={K(λ)² +L(λ)²}/2  (2)Tc(λ)=K(λ)×L(λ)  (3)wherein K(λ) is the spectral transmittance obtained when linearlypolarized light is applied in the direction of the transmission axis ofthe polarizing plate, L(λ) is the spectral transmittance obtained whenlinearly polarized light is applied in the direction of the absorptionaxis of the polarizing plate.

Both K(λ) and L(λ) were measured with a spectrophotometer (ShimadzuUV-2200).

Luminosity corrected transmittance T (luminosity corrected singletransmittance Ts, luminosity corrected parallel transmittance Tp,luminosity corrected cross transmittance Tc) was calculated from thespectral transmittance τ(λ) (Ts(λ), Tp(λ) Tc(λ)), which is measuredevery 10 nm in the wavelength range of 400 nm to 700 nm using expression(4) below.

$\begin{matrix}{T = \frac{\int_{400}^{700}{{P(\lambda)}{y(\lambda)}{\tau(\lambda)}\ {\mathbb{d}\lambda}}}{\int_{400}^{700}{{P(\lambda)}{y(\lambda)}\ {\mathbb{d}\lambda}}}} & (4)\end{matrix}$wherein P(λ) is the spectral distribution of standard light (Cilluminant) and y(λ) is the two-degree-field color matching function.

The degree of polarization P was calculated from the luminositycorrected parallel transmittance Tp and the luminosity corrected crosstransmittance Tc using expression (5) below.P={(Tp−Tc)/(Tp+Tc)}^(1/2)  (5)

Example 1

A surface of a polyethylene terephthalate film (obtained from TorayIndustries, Inc.) having a thickness of about 75 μm was rubbed with avelvet cloth on a rubbing apparatus by five reciprocating motions of thecloth. An aqueous solution containing a dye having a tabular molecularshape (“LCP N013” obtained from Optiva, Inc.) was applied to the rubbedsurface with No. 3 Meyer bar at an applying speed of 100 mm/sec, andthen left to stand at room temperature (about 20° C.) for 30 minutes fordrying. The thickness of the polarizing layer after drying was about 500nm. The overall thickness of the obtained polarizing plate is 75.5 μm.The degree of polarization P of the resultant polarizing plate was 84.0%and the single transmittance Ts thereof was 41.2%, exhibiting goodpolarizing performance.

Comparative Example 1

A polarizing plate was produced in the same manner as that in Example 1except that the surface of the polyethylene terephthalate film was notrubbed. The degree of polarization P of the resultant polarizing platewas 80.1% and the single transmittance Ts thereof was 40.8%.

Example 2

A polarizing plate was produced in the same manner as that in Example 1except that the solution was applied with No. 5 Meyer bar at an applyingspeed of 200 mm/sec. The degree of polarization P of the resultantpolarizing plate was 94.4% and the single transmittance Ts thereof was36.0%, exhibiting good polarizing performance.

Comparative Example 2

A polarizing plate was produced in the same manner as that in Example 2except that the surface of the polyethylene terephthalate film was notrubbed. The degree of polarization P of the resultant polarizing platewas 90.8% and the single transmittance Ts thereof was 36.3%.

Example 3

A surface of a norbornene resin film “SCA50” (obtained from SekisuiChemical Co., Ltd.) having a thickness of about 50 μm is rubbed with avelvet cloth on a rubbing apparatus by five reciprocating motions of thecloth. An aqueous solution containing a dye having a tabular molecularshape “LCP N0015” (obtained from Optiva, Inc.) is applied to the rubbedsurface with No. 5 Meyer bar coater at an applying speed of 50 mm/sec,and then left to stand at room temperature (about 20° C.) for 30 minutesfor drying to obtain a polarizing plate. The thickness of thethus-obtained polarizing layer is about 1000 nm. Aluminum is evaporatedonto the surface of the polarizing layer-formed film opposite to thesurface on which the polarizing layer is formed, forming a reflectinglayer having a thickness of about 60 nm. As a result, a thinnerreflective polarizing plate having a thickness of about 51 μm isobtained.

A diffusion type adhesive is applied to the surface of the polarizinglayer of the reflective polarizing plate, and the polarizing plate isbonded to the bottom surface of a TN liquid crystal cell via theadhesive. A polarizing plate comprising polyvinyl alcohol and iodine(“SQ1852A” obtained from Sumitomo Chemical Co., Ltd.) is bonded to thetop surface of the TN liquid crystal cell via an adhesive, to complete aTN liquid crystal display device. This TN liquid crystal display devicecan be thinned, and is small in parallax providing easy view.

Comparative Example 3

A TN liquid crystal display device was manufactured in the same manneras that in Example 3 except that a lamination (thickness: about 255 μm)of a polarizing plate comprising polyvinyl alcohol and iodine(“SQ12852A” obtained from Sumitomo Chemical Co., Ltd.), and a reflectingplate comprising silver was used as the polarizing plate bonded to thebottom surface of the TN liquid crystal cell. The resultant TN liquidcrystal display device was large in parallax and thus difficult to beviewed.

Thus, according to the present invention, a thinner polarizing platewith a high degree of polarization is attained. Therefore, thepolarizing plate of the present invention is suitably applicable toportable electronic equipment such as cellular phones, portableinformation terminals, smart cards and IC cards.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A polarizing plate comprising a polarizing layer having a thicknessof about 20 nm to about 1500 nm formed by rubbing at least one surfaceof a substrate, coating the rubbed surface of the substrate with anaqueous solution containing a dye having a tabular molecular shape, anddrying the solution, wherein the dye having a tabular molecular shapecoated on the rubbed surface of the substrate is oriented roughlyperpendicular to the rubbing direction, wherein the aqueous solutioncontaining a dye is prepared by introducing at least one hydrophilicgroups to the dye and solving the resultant dye to water.
 2. Thepolarizing plate according to claim 1, wherein the dye is at least onedyes selected from the group consisting of an anthraquinone type dye, aphthalocyanine type dye, a porphyrin type dye, a naphthalocyanine typedye, a quinacridone type dye, a dioxadin type dye, an indanthrene typedye, an acridine type dye, a perylene type dye, a pyrazolone type dye,an acridone type dye, a pyranthrone type dye and an isoviolanthrone typedye.
 3. The polarizing plate according to claim 1, wherein the substrateis a polyester resin film.
 4. A liquid crystal display device comprisingthe polarizing plate according to claim 1 laminated on a liquid crystalcell with the polarizing layer being positioned closer to the liquidcrystal cell.
 5. The liquid crystal display device according to claim 4,wherein a front polarizing plate is placed on a surface of the liquidcrystal cell opposite to the surface on which the polarizing plate islaminated.
 6. The liquid crystal display device according to claim 5,wherein the front polarizing plate is the same as the polarizing plateplaced opposite to the liquid crystal cell.